To date, there are no efficient semiconductor light emitters known that operate in the green, yellow and amber wavelengths, leading to the so-called green gap in photonics. The underlying challenges include the presence of large densities of defects and dislocations, due to the large lattice mismatch between InN and GaN, as well as the quantum-confined Stark effect. Use of the Purcell effect to bridge the green gap in photonics was predicted nearly two decades ago but has never materialized. Previous studies have been only focused on optical cavities in the order of micrometers, whereas practical LED devices require extended optical mode spread over the millimeter scale, i.e., three to six orders of magnitude larger than that of conventional designs.
The group of Prof. Zetian Mi at the University of Michigan (MI, USA) and the McGill University (Montreal, Canada) report the selective area epitaxy of InGaN photonic crystal structuresin their recent publication in Advanced Functional Materials. Dot-in-nanowires, nano-triangles and nano-rectangles are shown with precisely controlled size, spacing, and morphology, and form the fundamental building blocks of large area InGaN photonic crystal light emitters. The luminescence emission, in terms of both the peak position as well as spectral line widths, remain virtually invariant in the temperature range of 5 K to 300 K and under a wide range of excitation power.
Such distinct emission characteristics stem directly from the strong Purcell effect, due to the efficient coupling of the spontaneous emission to the highly stable and scalable band edge modes of InGaN photonic crystals, and are ideally suited for uncooled, high efficiency light-emitting-diode and laser operation.
This text was kindly provided by the authors.